1. Field of the Invention
The present invention relates to a plasma display device which controls signal processing in response to the signal format of an input signal.
2. Description of the Background Art
A plasma display panel (PDP) has been hithertofore known as one of the flat panel displays and received much attention as an alternative to a cathode ray tube (CRT).
Displaying an input video signal on a PDP requires the conversion of the video signal into pixel-by-pixel digital image data. Each pixel corresponds to a discharge cell which is a unit of discharge in the PDP. Gradation control at each discharge cell is such that a field is divided into subfields based on the number of gradation levels and luminescence or non-luminescence in each of the subfields is controlled. For example, if digital data indicative of a gradation level at each discharge cell is 6-bit digital data (64-level gradation), one field is divided into six subfields, and luminescence or non-luminescence in each of the six subfields is controlled depending on whether each bit is xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d. The luminance at each discharge cell corresponds to the digital data by setting the ratio of the number of sustain pulses in each of the subfields to 25 (MSB) to 20 (LSB). Thus, the increase in the number of subfields increases the number of gradation levels to achieve smooth display having improved gradation properties.
The luminescence or non-luminescence at each discharge cell is controlled in a manner described below. First, a priming pulse is applied to force a discharge to be produced at all discharge cells and to erase wall charges. Then, a scan pulse is applied to a scan electrode and an address pulse is selectively applied to an address electrode depending on display data to control whether to provide wall charges or not. This determines whether to cause luminescence at the associated discharge cell using a subsequent sustain pulse or not. At this time, reliable luminescence and enhanced display stability are achieved by increasing the pulse width of the scan pulse to prolong write time for providing the wall charges.
The division of one field into subfields for display control at each discharge cell as above described presents a problem in that a pseudo contour is produced when a moving picture is displayed. Specifically, an observer that follows a moving picture with his or her eyes finds the pseudo contour produced in a section of an image where the gradation should change smoothly. To prevent this, it has been proposed to subdivide a predetermined number of subfields to alleviate the moving picture pseudo contour.
The above described control accomplishes multi-level gradation display, high-luminance display, stable luminescence, prevention of moving picture pseudo contours and the like in the PDP image display.
The time required for one field is a fixed value determined by an input signal dependent upon a signalling system such as NTSC, PAL, and VGA, and is generally 16 to 20 msec. The above described control must be performed within this limited length of time. Unfortunately, time is insufficient for the control that satisfies overall performance. Specifically, the increase in the number of subfields, the elongation of the write time, and the subdivision of the subfields require accordingly longer time for one-field display, resulting in the insufficient execution of the above described control.
Further, signals are classified depending on the signal format, for example, into an interlaced scanning signal (referred to hereinafter as an xe2x80x9cinterlace signalxe2x80x9d) and a non-interlaced scanning signal (referred to hereinafter as a xe2x80x9cnon-interlace signalxe2x80x9d). The PDP which fundamentally uses the non-interlace signals for display is required to perform an interpolation process on the interlace signals to convert the interlace signals into the non-interlace signals. The interpolation process includes, for example, producing an intermediate horizontal line signal from two horizontal line signals, an upper and a lower. Disclosed in Japanese Patent Application Laid-Open No. P05-216433A (1993) is a simple process for driving the PDP so that one field of the interlace signal is displayed in a pair of lines, thereby to display the interlace signal, without using the conversion into the non-interlace signal by signal processing. This technique enables a pair of lines to be written at a time, reducing the time required for the write operation by half, but renders a displayed image rough on the whole since the same signal is displayed in the pair of lines. The use of this drive process requires the PDP to be used specifically for an interlace signal input and to fail to display the non-interlace signals such as VGA.
The time required for one field differs depending on the signal format of the input signal such as an NTSC system, a PAL system, VGA, and XGA. The level of the luminance in the plasma display is generally proportional to the frequency of the sustain pulse. Thus, changes in vertical synchronization frequency change the frequency of the sustain pulse depending on the signal format of the input signal, thereby changing the maximum luminance.
The amount of power consumption in the plasma display is proportional to the product of an APL (Average Picture Level) and the luminance. The APL is defined to mean a numerical value obtained by averaging the gradation levels (%) of all cells. For instance, the APL is 0% if black is displayed on the full screen, and is 100% if the highest gradation level of white is displayed on the full screen. The APL of a typical image is said to be an average of about 30 to 40%.
Thus, the increase in the frequency of the sustain pulse for higher luminance is not a problem for a typical screen but results in the increase in power consumption for a special screen, for example, a screen on which white is fully displayed. Countermeasures against this problem include APC (Automatic Power Control) which controls the luminance depending on the APL to suppress the power consumption at a fixed level or lower. This method is capable of suppressing maximum power consumption at a fixed level or lower on a typical screen while maintaining a high luminance, but presents another problem when a graphic signal (VGA, XGA and the like) from a personal computer is displayed. When a fixed screen (still picture) having a low APL is displayed in the form of a graphic signal, particular cells that continue high-luminance display are deteriorated, resulting in burning (image sticking on the screen).
Furthermore, in the PDP, a priming discharge (discharge at all cells) based on a priming pulse is carried out, for example, once for each subfield in order to enhance the discharge stability of the PDP. However, the priming discharge involves applying discharges to all discharge cells on the full screen at once to cause luminescence corresponding to a certain gradation level, resulting in low contrast. On the other hand, the decrease in the frequency of generation of the priming pulse leads to low discharge stability.
According to a first aspect of the present invention, a plasma display device comprises: control signal output means for outputting a control signal responsive to the signal format of an input video signal; and driving means for driving a plasma display panel based on the control signal outputted from the control signal output means.
Preferably, according to a second aspect of the present invention, the plasma display device of the first aspect further comprises: signal format identifying means for identifying the signal format of the input video signal, the signal format identifying means applying to the control signal output means an identification output responsive to the signal format of the input video signal.
Preferably, according to a third aspect of the present invention, in the plasma display device of the second aspect, the control signal output means includes selecting means for selecting one of a plurality of previously determined pieces of control information based on the identification output; and the control signal is provided based on the selected piece of control information.
Preferably, according to a fourth aspect of the present invention, in the plasma display device of the third aspect, the pieces of control information include the number of subfields which is previously determined in response to the signal format of the input video signal; and one field time period is divided into subfield time periods the number of which equals the number of subfields for representation of gradation.
Preferably, according to a fifth aspect of the present invention, in the plasma display device of the third aspect, the pieces of control information include frequency with which a priming pulse is generated per field, the frequency being previously determined in response to the signal format of the input video signal.
Preferably, according to a sixth aspect of the present invention, in the plasma display device of the fourth aspect, whether or not to divide the one field time period into the subfield time periods the number of which is greater than the minimum number of subfields required to represent the gradation in order to prevent a pseudo contour of a moving picture is controlled in response to the signal format of the input video signal.
Preferably, according to a seventh aspect of the present invention, in the plasma display device of the third aspect, the pieces of control information include a set value for write time per cell, the set value for write time being previously determined in response to the signal format of the input video signal; and a write operation of data into the plasma display panel is controlled based on the set value for write time.
Preferably, according to an eighth aspect of the present invention, in the plasma display device of the third aspect, the pieces of control information include the number of sustain pulses per field for an APL, the number of sustain pulses being previously determined in response to the signal format of the input video signal; and APC characteristics are changed based on the number of sustain pulses.
Preferably, according to a ninth aspect of the present invention, in the plasma display device of the third aspect, the pieces of control information include the number of sustain pulses per field, the number of sustain pulses being previously determined in response to the signal format of the input video signal.
Preferably, according to a tenth aspect of the present invention, in the plasma display device of the third aspect, the pieces of control information include color temperature conversion characteristics of image data, the color temperature conversion characteristics being previously determined in response to the signal format of the input video signal.
According to an eleventh aspect of the present invention, a method of driving a plasma display comprises the steps of: outputting a control signal in response to the signal format of an input video signal; and driving a plasma display panel based on the control signal.
Preferably, according to a twelfth aspect of the present invention, in the method of the eleventh aspect, the control signal is generated based on an identification output responsive to the signal format of the input video signal.
Preferably, according to a thirteenth aspect of the present invention, in the method of the twelfth aspect, the control signal is provided based on one piece of control information selected in response to the identification output among a plurality of previously prepared pieces of control information.
Preferably, according to a fourteenth aspect of the present invention, in the method of the thirteenth aspect, the pieces of control information include the number of subfields which is previously determined in response to the signal format of the input video signal; and one field time period is divided into subfield time periods the number of which equals the number of subfields for representation of gradation.
Preferably, according to a fifteenth aspect of the present invention, in the method of the thirteenth aspect, the pieces of control information include frequency with which a priming pulse is generated per field, the frequency being previously determined in response to the signal format of the input video signal.
Preferably, according to a sixteenth aspect of the present invention, in the method of the fourteenth aspect, whether or not to divide the one field time period into the subfield time periods the number of which is greater than the minimum number of subfields required to represent the gradation in order to prevent a pseudo contour of a moving picture is controlled in response to the signal format of the input video signal.
Preferably, according to a seventeenth aspect of the present invention, in the method of the thirteenth aspect, the pieces of control information include a set value for write time per cell, the set value for write time being previously determined in response to the signal format of the input video signal; and a write operation of data into the plasma display panel is controlled based on the set value for write time.
Preferably, according to an eighteenth aspect of the present invention, in the method of the thirteenth aspect, the pieces of control information include the number of sustain pulses per field for an APL, the number of sustain pulses being previously determined in response to the signal format of the input video signal; and APC characteristics are changed based on the number of sustain pulses.
Preferably, according to a nineteenth aspect of the present invention, in the method of the thirteenth aspect, the number of sustain pulses is in inverse proportion to the frequency of a vertical synchronization signal in the input video signal.
Preferably, according to a twentieth aspect of the present invention, in the method of the thirteenth aspect, the pieces of control information include color temperature conversion characteristics of image data, the color temperature conversion characteristics being previously determined in response to the signal format of the input video signal.
In accordance with the first aspect of the present invention, the control signal responsive to the signal format of the input video signal is outputted, and the PDP is driven based on the control signal. Thus, the PDP may be driven under different driving conditions for each signal format of the input video signal. The PDP may be optimally driven in response to individual video signals while taking full advantage of higher-priority characteristics determined by the input video signal under various restrictive conditions presented when the input video signal is displayed on the PDP (e.g., the sequence time which is originally required for optimum display on the PDP is limited by the video signal; a luminance and the suppression of the degree of sticking conflict with each other; and display contrast and display stability conflict with each other).
In accordance with the second aspect of the present invention, the control signal output means outputs the control signal in response to and based on the signal format of the input video signal identified by the signal format identification means. This allows the plasma display to be automatically driven in response to the signal format of the input video signal.
In accordance with the third aspect of the present invention, the control signal is provided based on the selected one of the plurality of pieces of control information possessed by the control signal output means. The preparation of optimum driving conditions responsive to the signal format of the input video signal as the control information ensures the setting of the optimum driving conditions.
In accordance with the fourth aspect of the present invention, the gradation is represented by dividing the one field time period into the plurality of subfield time periods, and the number of subfields is determined according to the respective signal formats of the input video signal. Depending upon the signal format of the input video signal, the number of gradation levels is preferably greater in some cases, and need not be so great in other cases. The optimum number of gradation levels may be set in accordance with such requirements. In particular, the setting of a greater number of gradation levels allows smooth display, and the setting of a smaller number of gradation levels provides a resultant time margin to be used to enhance other characteristics.
In accordance with the fifth aspect of the present invention, the frequency with which the priming pulse is generated per field is set in response to the signal format of the input video signal. Depending on the signal format of the input video signal, the contrast is preferably high in some cases and need not be so high in other cases. Further, flicker is conspicuous in some cases and is not so conspicuous in other cases. The fifth aspect of the present invention provides an optimum display image (e.g., an image having not so high contrast but high display stability with less flicker, or an image having not so high display stability but high contrast) for each signal format of the input video signal as the case may be.
In accordance with the sixth aspect of the present invention, whether or not to divide the one field time period into the subfield time periods the number of which is greater than the minimum number of subfields required to represent the gradation in order to prevent the pseudo contour of the moving picture is controlled in response to the signal format of the input video signal. Depending on the signal format of the input video signal, the moving picture pseudo contour is a significant problem in some cases and is not so significant in other cases. As the case may be, the moving picture pseudo contour is suppressed in response to the input video signal for which the pseudo contour is the problem, and measures against the moving picture pseudo contour need not be taken in response to the input video signal for which the pseudo contour is not so significant. The time margin provided by the non-execution of the measures against the moving picture pseudo contour may be used to enhance other characteristics.
In accordance with the seventh aspect of the present invention, the write time per cell during the write operation of data into the PDP is previously determined in response to the signal format of the input video signal. Depending on the signal format of the input video signal, flicker is a significant problem in some cases and is not so significant in other cases. For the input video signal for which flicker is the significant problem, the write time is elongated to increase the display stability, providing the image with less flicker. For the input video signal for which flicker is not so significant, the write time may be shortened, and the resultant time margin may be used to enhance other characteristics.
In accordance with the eighth aspect of the present invention, the number of sustain pulses per field for the APL is previously determined in response to the signal format of the input video signal. For the input video signal for which burning is a significant problem, the APC characteristics are changed so that the peak luminance is suppressed to prevent the sticking. For the input video signal for which the burning is not so significant, the APC characteristics are changed so that the peak luminance is increased to provide a well-contrasted image.
In accordance with the ninth aspect of the present invention, the number of sustain pulses per field is changed in response to the signal format of the input video signal. Thus, the screen is displayed with a luminance suitable for the input video signal.
In accordance with the tenth aspect of the present invention, the characteristics of color temperature conversion processing performed on image data are changed in response to the signal format of the input video signal. This provides an image having the optimum relationship between the color temperature and the luminance in response to the signal format of the input video signal under such PDP display restrictive conditions that the increase in color temperature requires the decrease in luminance.
In accordance with the eleventh aspect of the present invention, the control signal responsive to the signal format of the input video signal is outputted, and the PDP is driven based on the control signal. Thus, the PDP may be driven under different driving conditions for each signal format of the input video signal. The PDP may be optimally driven in response to individual video signals while taking full advantage of higher-priority characteristics determined by the input video signal under various restrictive conditions presented when the input video signal is displayed on the PDP (e.g., the sequence time which is originally required for optimum display on the PDP is limited by the video signal; the luminance and the suppression of the degree of sticking conflict with each other; and the display contrast and the display stability conflict with each other).
In accordance with the twelfth aspect of the present invention, the control signal is generated based on the identification output responsive to the signal format of the input video signal. This allows the plasma display to be automatically driven in response to the signal format of the input video signal.
In accordance with the thirteenth aspect of the present invention, the control signal is provided based on the selected one of the plurality of pieces of control information. The preparation of optimum driving conditions responsive to the signal format of the input video signal as the control information ensures the setting of the optimum driving conditions.
In accordance with the fourteenth aspect of the present invention, the gradation is represented by dividing the one field time period into the plurality of subfield time periods, and the number of subfields is determined according to the respective signal formats of the input video signal. Depending upon the signal format of the input video signal, the number of gradation levels is preferably greater in some cases, and need not be so great in other cases. The optimum number of gradation levels may be set in accordance with such requirements. In particular, the setting of a greater number of gradation levels allows smooth display, and the setting of a smaller number of gradation levels provides a resultant time margin to be used to enhance other characteristics.
In accordance with the fifteenth aspect of the present invention, the frequency with which the priming pulse is generated per field is set in response to the signal format of the input video signal. Depending on the signal format of the input video signal, the contrast is preferably high in some cases and need not be so high in other cases. Further, flicker is conspicuous in some cases and is not so conspicuous in other cases. The seventeenth aspect of the present invention provides an optimum display image (e.g., an image having not so high contrast but high display stability with less flicker, or an image having not so high display stability but high contrast) for each signal format of the input video signal as the case may be.
In accordance with the sixteenth aspect of the present invention, whether or not to divide the one field time period into the subfield time periods the number of which is greater than the minimum number of subfields required to represent the gradation in order to prevent the pseudo contour of the moving picture is controlled in response to the signal format of the input video signal. Depending on the signal format of the input video signal, the moving picture pseudo contour is a significant problem in some cases and is not so significant in other cases. As the case may be, the moving picture pseudo contour is suppressed in response to the input video signal for which the pseudo contour is the problem, and measures against the moving picture pseudo contour need not be taken in response to the input video signal for which the pseudo contour is not so significant. The time margin provided by the non-execution of the measures against the moving picture pseudo contour may be used to enhance other characteristics.
In accordance with the seventeenth aspect of the present invention, the write time per cell during the write operation of data into the PDP is previously determined in response to the signal format of the input video signal. Depending on the signal format of the input video signal, flicker is a significant problem in some cases and is not so significant in other cases. For the input video signal for which flicker is the significant problem, the write time is elongated to increase the display stability, providing the image with less flicker. For the input video signal for which flicker is not so significant, the write time may be shortened, and the resultant time margin may be used to enhance other characteristics.
In accordance with the eighteenth aspect of the present invention, the number of sustain pulses per field for the APL is previously determined in response to the signal format of the input video signal. For the input video signal for which burning is a significant problem, the APC characteristics are changed so that the peak luminance is suppressed to prevent the sticking. For the input video signal for which burning is not so significant, the APC characteristics are changed so that the peak luminance is increased to provide a well-contrasted image.
In accordance with the nineteenth aspect of the present invention, the number of sustain pulses per field is changed in response to the signal format of the input video signal. Thus, the screen is displayed with a luminance suitable for the input video signal.
In accordance with the twentieth aspect of the present invention, the characteristics of color temperature conversion processing performed on image data are changed in response to the signal format of the input video signal. This provides an image having the optimum relationship between the color temperature and the luminance in response to the signal format of the input video signal under such PDP display restrictive conditions that the increase in color temperature requires the decrease in luminance.
It is therefore an object of the present invention to provide a plasma display device and a method of driving a plasma display which provide better display control in response to the signal format of an input signal.